Quantitative Evaluation of Adult Subglottic Stenosis Using Intraoperative Long-range Optical Coherence Tomography

A review on diagnostic assessments of tracheal stenosis

Tracheal stenosis (TS) is a pathological condition characterized by a reduction in the trachea diameter. It is a common complication after prolonged endotracheal intubation but may also arise from autoimmune or inflammatory processes. Clinicians can select the most appropriate treatment option based on individual patient conditions. Therefore, precise localization and evaluation of the stenosis are essential to ensure safe and effective treatment. This review summarizes current research on TS diagnosis and assessment, encompassing functional, imaging, and bronchoscopy methods. The characteristics, advantages, and disadvantages of each technique are discussed in relation to their application in the diagnosis and assessment of TS. Bronchoscopy is considered the cornerstone of TS diagnosis, and novel adjunct imaging modalities have emerged to enhance its accuracy. We explore advanced endomicroscopic methods, such as endobronchial ultrasound (EBUS), photoacoustic endoscopy (PAE), optical coherence tomography (OCT), and confocal laser endomicroscopy (CLE). Among these, EBUS is clinically approved for diagnosing lesions with high resolution and acceptable penetration depth. OCT and CLE offer real-time imaging for peripheral lesions and potentially malignant nodules, but their use is limited by cost and availability in low-resource settings. Therefore, bronchoscopy, with biopsy techniques as needed, remains the optimal approach for diagnosing tracheal stenosis.

Assessing the interrater and intrarater reliability of subglottic stenosis grading systems

BACKGROUND

Subglottic stenosis (SGS) is a condition leading to narrowing of the upper airway which can lead to dyspnea and life-threatening airway obstruction. Although other proposed grading systems exist, the Cotton Myer (CM) and percent stenosis systems are the most widespread in clinical practice. Despite this, the CM system has not yet been validated for visual assessment of SGS.

OBJECTIVE

To determine the interrater and intrarater reliability of the CM grading system among a cohort of physicians who manage patients with SGS.

METHODS

An online survey created with videos of tracheoscopies from 20 adult patients with subglotticstenosis (SGS) was sent individually to 9 expert physicians from various medical specialties, all of whom managed patients with SGS. Physicians were asked to view the 20 tracheoscopy videos and assess both the percent stenosis and Cotton Myer (CM) grade of each patient. After a period of 4 weeks, the physicians were sent the same survey of the 20 tracheoscopy videos. The interrater and intrarater reliability was calculated using the intraclass correlation coefficient (ICC), a measurement used to evaluate the reliability (the extent to which a measurement can be replicated) of two or more raters measuring the same subject.

RESULTS

Overall, CM and percent stenosis systems were found to have an ICC of 0.94 and 0.90 within the domain of interrater reliability, respectively, and ICC of 0.71 and 0.81 within the domain of intrarater reliability, respectively.

CONCLUSION

Our findings suggest that the CM and percent stenosis grading systems remain a valid clinical tool to measure and communicate the severity of airway obstruction in SGS.

Long-range optical coherence tomography of pediatric airway during drug induced sleep endoscopy: A preliminary report

OBJECTIVE

Drug induced sleep endoscopy (DISE) is often performed for pediatric obstructive sleep apnea (OSA) when initial diagnostic studies do not provide adequate information for therapy. However, DISE scoring is subjective and with limitations. This proof-of-concept study demonstrates the use of a novel long-range optical coherence tomography (LR-OCT) system during DISE of two pediatric patients.

METHODS

LR-OCT was used to visualize the airway of pediatric patients during DISE. At the conclusion of DISE, the OCT probe was guided in the airway under endoscopic visual guidance, and cross-sectional images were acquired at the four VOTE locations. Data processing involved image resizing and alignment, followed by rendering of three-dimensional (3D) volumetric models of the airways.

RESULTS

Two patients were included in this study. Patient one had 18.4%, 20.9%, 72.3%, and 97.3% maximal obstruction at velum, oropharynx, tongue base, and epiglottis, while patient two had 40.2%, 41.4%, 8.0%, and 17.5% maximal obstruction at these regions, respectively. Three-dimensional reconstructions of patients' airways were also constructed from the OCT images.

CONCLUSION

This proof-of-concept study demonstrates the successful evaluation of pediatric airway during DISE using LR-OCT, which accurately identified sites and degrees of obstruction with respective 3D airway reconstruction.

All-fiber probes for endoscopic optical coherence tomography of the large airways

Endoscopic optical coherence tomography of large airways poses unique challenges. A hybrid lens is described that consists of a section of coreless fiber and graded index fiber (GIF), followed by a ball lens section. This design produces low numerical aperture beams better suited for large airway imaging. The performance of this lens is compared against conventional GIF and ball lens designs. Forward- and side-viewing probes were modeled, fabricated, and tested. The impact of a sheath on the beam profile was also investigated. Probes with working distances larger than 10 mm and depth-of-focus exceeding 12 mm are demonstrated with the proposed design.

Evaluation of the Human Vocal Fold Lamina Propria Development Using Optical Coherence Tomography

OBJECTIVES/HYPOTHESIS

Identifying distinctive features of the vocal fold (VF) during development could have significant clinical implications for treating voice disorders. This study investigates the structural organization of the VF microanatomy across gender and age groups using optical coherence tomography (OCT).

STUDY DESIGN

Prospective clinical trial.

MATERIALS AND METHODS

In vivo OCT images were acquired from 97 patients (58 males and 39 females) aged between 6 weeks and 27 years. All patients showed no signs of vocal fold pathology on endoscopy. Morphological features were extracted from OCT images and statistically compared between age groups. This study was performed at Massachusetts Eye and Ear between 2017 and 2019.

RESULTS

All OCT acquisitions show a stratified microanatomy across age groups, even in newborns suggesting the presence of a superficial lamina propria (SLP) at birth. Furthermore, the optical scattering in the VF lamina propria changes according to age, suggesting subepithelial maturation. Although the epithelium thickness was relatively constant across age groups, the SLP showed a significant linear relationship between age and thickness (P = .016). Furthermore, a significant difference (P = .002) in SLP thickness was found between young adult males and females. The overall thickness of the entire mucosa did not change significantly with age.

CONCLUSION

OCT is a noninvasive imaging modality capable of providing quantitative morphological features to describe the VF development. A stratified structure can be observed in OCT from newborns to young adults. Further investigations could combine OCT, acoustic measurements, and molecular sensitive techniques to provide a complete interpretation of the VF development.

LEVEL OF EVIDENCE

NA Laryngoscope, 131:E2558-E2565, 2021.

Quantitative evaluation of the human vocal fold extracellular matrix using multiphoton microscopy and optical coherence tomography

Identifying distinct normal extracellular matrix (ECM) features from pathology is of the upmost clinical importance for laryngeal diagnostics and therapy. Despite remarkable histological contributions, our understanding of the vocal fold (VF) physiology remains murky. The emerging field of non-invasive 3D optical imaging may be well-suited to unravel the complexity of the VF microanatomy. This study focused on characterizing the entire VF ECM in length and depth with optical imaging. A quantitative morphometric evaluation of the human vocal fold lamina propria using two-photon excitation fluorescence (TPEF), second harmonic generation (SHG), and optical coherence tomography (OCT) was investigated. Fibrillar morphological features, such as fiber diameter, orientation, anisotropy, waviness and second-order statistics features were evaluated and compared according to their spatial distribution. The evidence acquired in this study suggests that the VF ECM is not a strict discrete three-layer structure as traditionally described but instead a continuous assembly of different fibrillar arrangement anchored by predominant collagen transitions zones. We demonstrated that the ECM composition is distinct and markedly thinned in the anterior one-third of itself, which may play a role in the development of some laryngeal diseases. We further examined and extracted the relationship between OCT and multiphoton imaging, promoting correspondences that could lead to accurate 3D mapping of the VF architecture in real-time during phonosurgeries. As miniaturization of optical probes is consistently improving, a clinical translation of OCT imaging and multiphoton imaging, with valuable qualitative and quantitative features, may have significant implications for treating voice disorders.

Principles of Subglottic and Tracheal Visualization with Transnasal Flexible Laryngoscopy

OBJECTIVE

The subglottic area and trachea are important parts of the upper airway, and can be visualized easily using transnasal flexible laryngoscopy (TFL). The aim of this study was to develop a clinical grading system to assist in documentation of the subglottic area and trachea with TFL, and to demonstrate the basic principles of visualization of these anatomic areas as a laryngology practice.

METHODS

The TFL videos of 100 randomized patients were evaluated by three laryngologists. The simple head extension (SHE) position and flexion position (FP) were applied to the patients during the visualization of the subglottic area and trachea. A paired t test was used to compare the grades of the subglottic and tracheal view according to the SHE and FP scores.

RESULTS

This study examined 50 male and 50 female patients ranging in age from 28 to 83 years (mean age: 50.09 ± 13.05 years). For the SHE and FP, the numbers of patients constituting grade 1 were 2 and 35, grade 2 were 2 and 37, grade 3 were 30 and 19, and grade 4 were 41 and 9, respectively. There was a statistically significant difference between SHE and FP (P  <  0.05). The k score was 0.785 between the ratings of observer 1 and observer 2; 0.771 between observer 1 and observer 3; and 0.757 between observer 2 and observer 3 (P  <  0.001).

CONCLUSION

This new grading system for the visualization of the subglottis and trachea can help physicians assess and identify the upper airways, and FP provides a better subglottic and tracheal view than SHE.

Pediatric dysphonia: It's not about the nodules

OBJECTIVE

Despite the fact that vocal nodules are the most common cause of chronic dysphonia in children, uncertainty and lack of consensus complicates practically every diagnostic and management decision. Selecting an optimal staging system is fundamental to understanding a disease process, mandatory for uniform reporting, and crucial to predicting natural history and treatment outcomes. The ideal prognostic model for vocal nodules is under intense debate. The purpose of this study was to analyze the predictive power of vocal nodule grade to severity of voice metrics in children.

METHODS

Seventy-nine patients diagnosed with vocal cord nodules between 2006 and 2012 were drawn from UPMC Children's Hospital of Pittsburgh Voice, Resonance and Swallowing Center Research Registry. Subject age at time of diagnosis, nodule grade, relevant co-morbidities, scores on The Consensus Auditory-Perceptual Evaluation of Voice (CAPE-V), parent-reported Pediatric Voice Handicap Index (pVHI), the phonotraumatic behaviors profile, habitual speaking pitch fundamental frequencies, pitch range, volume intensity, and s/z ratio were recorded and compiled into a de-identified database for analysis.

RESULTS

Based on the Kruskal-Wallis H Test, there was no statistically significant correlation between nodule grade and total pitch range (p = .21), s/z ratio (p = .50), volume intensity (p = .33), overall CAPE-V Scores (p = .15), or pVHI Scores (p = .29). Chi-squared tests also revealed no significant associations between nodule grade and abnormality in habitual speaking pitch (p = .14 for fundamental frequency while sustaining a vowel sound, p = .37 for fundamental frequency while speaking structured tasks i.e. counting, or p = .76 while speaking in conversation).

CONCLUSION

The current "gold-standard" for grading vocal nodule size suggests that the nodules themselves are not driving the standard dysphonic metrics that are most commonly collected and monitored in such children. This outcome is consistent with other studies reporting similar findings and was expected based on the inconsistencies in the reported literature to date. By extension, the conventional wisdom of avoiding surgical treatment of vocal nodules in children seems prudent as there is little evidence to suggest that the nodules themselves are "driving" the severity of the dysphonia. Ultimately identifying the true "drivers" of dysphonia in children will suggest alternative therapies that are more specific and directed to the pathophysiology. Most pediatric voice care professionals will welcome such discoveries as those in the front line of patient care are often rendered helpless and frustrated.

Dynamic programming and automated segmentation of optical coherence tomography images of the neonatal subglottis: enabling efficient diagnostics to manage subglottic stenosis

Subglottic stenosis (SGS) is a challenging disease to diagnose in neonates. Long-range optical coherence tomography (OCT) is an optical imaging modality that has been described to image the subglottis in intubated neonates. A major challenge associated with OCT imaging is the lack of an automated method for image analysis and micrometry of large volumes of data that are acquired with each airway scan (1 to 2 Gb). We developed a tissue segmentation algorithm that identifies, measures, and conducts image analysis on tissue layers within the mucosa and submucosa and compared these automated tissue measurements with manual tracings. We noted small but statistically significant differences in thickness measurements of the mucosa and submucosa layers in the larynx (p  <  0.001), subglottis (p  =  0.015), and trachea (p  =  0.012). The automated algorithm was also shown to be over 8 times faster than the manual approach. Moderate Pearson correlations were found between different tissue texture parameters and the patient’s gestational age at birth, age in days, duration of intubation, and differences with age (mean age 17 days). Automated OCT data analysis is necessary in the diagnosis and monitoring of SGS, as it can provide vital information about the airway in real time and aid clinicians in making management decisions for intubated neonates.

Real-time robotic airway measurement: An additional benefit of a novel steady-hand robotic platform

OBJECTIVE

Describe the secondary capability of a robotic system to provide real-time measurements of airway dimensions with high fidelity.

METHODS

Seven unique phantoms of laryngotracheal stenosis (LTS) were modeled using a computer-aided design tool and were three dimensionally printed. These stenoses were of different dimensions and orientations, and some were purposefully oblique. The dimensions of the stenoses were then measured with the novel Robotic ENT (Ear, Nose, and Throat) Microsurgery System (REMS; Galen Robotics, Inc., Sunnyvale, CA) because it is capable of tool position memory in three dimensional (3D) space. Five participants (two laryngologists, two otolaryngology-head and neck surgery residents, one neurotology fellow) measured each axis of stenosis (anteroposterior, lateral, and craniocaudal) three times for each of the seven stenosis phantoms. These measurements were then compared to the known design dimensions. Mean magnitude of error (MOE) and interrater reliability (IRR) using an intraclass correlation coefficient (ICC) were then calculated.

RESULTS

Mean MOE and standard deviation for all measurements was 0.306 ± 0.247 mm. Mean MOE was 0.374 ± 0.292 mm, 0.300 ± 0.237 mm, and 0.244 ± 0.185 mm for the anteroposterior, lateral, and craniocaudal dimensions of stenosis, respectively. Eighty-two percent of all measurements had MOE < 0.5 mm. ICC was 0.945 (95% confidence interval [CI]: 0.847-0.989), 0.995 (95% CI: 0.984-0.999), and 0.993 (95% CI: 0.987-0.999) for anteroposterior, lateral, and craniocaudal dimensions, respectively, indicating excellent agreement among participants.

CONCLUSION

The REMS can be used to reliably and accurately measure airway dimensions in 3D regardless of the orientation of stenosis. This ability may be easily extrapolated to the measurement of any airway lesion during laryngotracheal surgery.

LEVEL OF EVIDENCE

4 Laryngoscope, 129:324-329, 2019.

Upper airway reconstruction using long-range optical coherence tomography: Effects of airway curvature on airflow resistance

OBJECTIVES

Adenotonsillectomy (AT) is commonly used to treat upper airway obstruction in children, but selection of patients who will benefit most from AT is challenging. The need for diagnostic evaluation tools without sedation, radiation, or high costs has motivated the development of long-range optical coherence tomography (LR-OCT), providing real-time cross-sectional airway imaging during endoscopy. Since the endoscope channel location is not tracked in conventional LR-OCT, airway curvature must be estimated and may affect predicted airway resistance. The study objective was to assess effects of three realistic airway curvatures on predicted airway resistance using computational fluid dynamics (CFD) in LR-OCT reconstructions of the upper airways of pediatric patients, before and after AT.

METHODS

Eight subjects (five males, three females, aged 4-9 years) were imaged using LR-OCT before and after AT during sedated endoscopy. Three-dimensional (3D) airway reconstructions included three airway curvatures. Steady-state, inspiratory airflow simulations were conducted under laminar conditions, along with turbulent simulations for one subject using the k-ω turbulence model. Airway resistance (pressure drop/flow) was compared using two-tailed Wilcoxon signed rank tests.

RESULTS

Regardless of the airway curvatures, CFD findings corroborate a surgical end-goal with computed post-operative airway resistance significantly less than pre-operative (P < 0.01). The individual resistances did not vary significantly for different airway curvatures (P > 0.25). Resistances computed using turbulent simulations differed from laminar results by less than ∼5%.

CONCLUSIONS

The results suggest that reconstruction of the upper airways from LR-OCT imaging data may not need to account for airway curvature to be predictive of surgical effects on airway resistance. Lasers Surg. Med. 51:150-160, 2019. © 2018 Wiley Periodicals, Inc.

Role of the impulse oscillometry in the evaluation of tracheal stenosis

INTRODUCTION AND OBJECTIVES

Tracheal stenosis is a rare and challenging disease. Bronchoscopy is the gold standard for diagnosis and assessment but brings inherent risks. Spirometry is commonly used to access obstructions but is not always feasible due to patient related factors. We therefore considered impulse oscillometry (IOS) as a non-invasive method to quantify airway obstruction and its potential use for diagnosis and follow-up of tracheal stenosis.

MATERIALS AND METHODS

Patients with confirmed tracheal stenosis were recruited between January 1st, 2015 and December 31st, 2016. Before bronchoscopy, all subjects underwent IOS and spirometry; for patients submitted to interventional bronchoscopy the same techniques were also performed after the procedure. We assessed the correlation between IOS measurements and airway narrowing as well as between IOS and spirometry values.

RESULTS

Twenty-one patients were included. Tracheal narrowing was inversely correlated with X5% (r -0.442, p 0.045) and positively correlated with FEV1/PEF (r 0.467, p 0.033). The stenosis length was inversely correlated with PEF and PEF% (r -0.729, p=0.001 and r -0.707, p=0.002, respectively). There was a strong correlation between spirometric and IOS values. We did not find any significant differences between pre- and post-intervention IOS values for patients assessed after interventional bronchoscopy.

CONCLUSIONS

Our study showed a weak correlation between X5% and tracheal narrowing making it unclear whether IOS can be used for physiological assessment of patients with tracheal stenosis. Stenosis length correlated with PEF making it a potential predictor of successful surgical approach. The correlation between IOS and spirometric values makes IOS a potential alternative in patients with suspected tracheal stenosis who are not able to perform spirometry. Larger scale studies should clarify the role of IOS in this pathology.

Quantifying Anatomic Deformations During Laryngoscopy

For a variety of head and neck cancers, specifically those of the oropharynx, larynx, and hypopharynx, minimally invasive trans-oral approaches have been developed to reduce perioperative and long-term morbidity. However, in trans-oral surgical approaches anatomical deformation due to instrumentation, specifically placement of laryngoscopes and retractors, present a significant challenge for surgeons relying on preoperative imaging to resect tumors to negative margins. Quantifying the deformation due to instrumentation is needed in order to develop predictive models of operative deformation. In order to study this deformation, we used a CT/MR-compatible laryngoscopy system in concert with intraoperative CT imaging. 3D models of preoperative and intraoperative anatomy were generated. Mandible and hyoid displacements as well as tongue deformations were quantified for eight patients undergoing diagnostic laryngoscopy. Across patients, we found on average 1.3 cm of displacement for these anatomic structures due to laryngoscope insertion. On average, the maximum displacement for certain tongue regions exceeded 4 cm. The anatomical deformations quantified here can serve as a reference for describing how the upper aerodigestive tract anatomy changes during instrumentation and may be helpful in developing predictive models of intraoperative upper aerodigestive tract deformation.

A Simple Endoscopic Technique for Measuring the Cross-Sectional Area of the Upper Airway in a Rabbit Model

OBJECTIVE

Validate an accurate and reproducible method of measuring the cross-sectional area (CSA) of the upper airway.

SUBJECTS AND METHODS

This is a prospective animal study done at a tertiary care medical treatment facility. Control images were obtained using endotracheal tubes of varying sizes. In vivo images were obtained from various timepoints of a concurrent study on subglottic stenosis. Using a 0° rod telescope, an instrument was placed at the level of interest, and a photo was obtained. Three independent and blinded raters then measured the CSA of the narrowest portion of the airway using open source image analysis software.

RESULTS

Each blinded rater measured the CSA of 79 photos. The t testing to assess for accuracy showed no difference between measured and known CSAs of the control images ( P = .86), with an average error of 1.5% (SD = 5.5%). All intraclass correlation (ICC) values for intrarater agreement showed excellent agreement (ICC > .75). Interrater reliability among all raters in control (ICC = .975; 95% CI, .817-.995) and in vivo (ICC = .846;, 95% CI, .780-.896) images showed excellent agreement.

CONCLUSIONS

We validate a simple, accurate, and reproducible method of measuring the CSA of the airway that can be used in a clinical or research setting.

Airway compliance measured by anatomic optical coherence tomography

Quantification of airway compliance can aid in the diagnosis and treatment of obstructive airway disorders by detecting regions vulnerable to collapse. Here we evaluate the ability of a swept-source anatomic optical coherence tomography (SSaOCT) system to quantify airway cross-sectional compliance (CC) by measuring changes in the luminal cross-sectional area (CSA) under physiologically relevant pressures of 10-40 cmH₂O. The accuracy and precision of CC measurements are determined using simulations of non-uniform rotation distortion (NURD) endemic to endoscopic scanning, and experiments performed in a simplified tube phantom and ex vivo porcine tracheas. NURD simulations show that CC measurements are typically more accurate than that of the CSAs from which they are derived. Phantom measurements of CSA versus pressure exhibit high linearity (R²>0.99), validating the dynamic range of the SSaOCT system. Tracheas also exhibited high linearity (R² = 0.98) suggestive of linear elasticity, while CC measurements were obtained with typically ± 12% standard error.